Embodiments relate generally to marine geophysical surveying and, more particularly, embodiments relate to methods for acquiring geophysical data by dynamically manipulating survey spread in response a change in distribution of a target.
Techniques for geophysical surveying include marine geophysical surveying, such as seismic surveying and electromagnetic surveying, in which geophysical data may be collected or acquired from below the Earth's surface. Geophysical surveying has applications in mineral and energy exploration and production to help identify locations of hydrocarbon-hearing formations. The formations of interest in the marine geophysical survey are commonly referred to as “targets.”
Certain types of marine geophysical surveying, such as seismic or electromagnetic surveying, may include towing an energy source at a selected depth in a body of water. One or more streamers also may be towed in the water at selected depths by the same or a different vessel. The streamers may be cables that include a plurality of geophysical sensors disposed thereon at spaced apart locations along the length of the cable. Some geophysical surveys locate sensors on ocean bottom cables or nodes in addition to, or instead of, streamers. The geophysical sensors may be operable to generate a signal that is related to a parameter being measured by the geophysical sensor. At selected times, the energy source may be actuated to generate, for example, seismic or electromagnetic energy that travels downwardly into the subsurface rock. Energy that interacts with interfaces, generally at the boundaries between layers of formations, may be returned toward the surface and detected by the geophysical sensors on the streamers. The detected energy may be used to infer certain properties of the target, such as structure, mineral composition and fluid content, thereby providing information useful in the recovery of hydrocarbons.
Current marine geophysical survey techniques may utilize multiple streamers towed at selected lateral distances from one another. Spreading devices are commonly used in geophysical surveying to achieve the desired lateral spread between the streamers. The spreading devices may include a variety of devices, such as doors, paravanes, and steering rudders, collectively referred to herein as “deflectors.” The layout of the streamers while being towed through the water is commonly referred to as the “streamer spread.” The marine geophysical survey may also include other towed equipment, such as the energy source. The layout of all the in-sea equipment, including the streamer spread, the energy source(s), and the deflectors, among other equipment, may be referred to herein as the “survey spread.” The survey spread, including the streamer spread, is typically determined prior to the marine geophysical survey by considering a number of factors, including without limitations, performance characteristics, financial considerations, and customer preference, among others. However, current techniques typically do not dynamically manipulate the survey spread during the marine geophysical survey to take advantage of and, thus, optimize acquired data.